Safety switches are used for monitoring the state of a safety device of a machine, for example, for monitoring the engaged state of a safety door of a safety enclosure for a machine tool or an industrial robot. When the safety device is in the engaged state, the safety switch can provide an enable signal for the operation of the machine. When the safety device is disengaged, the safety switch interrupts one or more electric circuits, for example, by an electrical contact pair that are actuated by positive locking or by an electronic switching element. The enable signal is then no longer provided. The associated machine can then be transferred to a safe operational state, for example it may be turned off, or the turning on of the machine may be prevented.
In some applications, the engaged state of the safety device is necessary to be detachably fixed, for example when, in an operational state of the machine, while the disengagement of the safety device is to be prevented. The fixation is only removed, and the safety device can only be disengaged, when the machine is at a complete standstill.
In the case of safety switches having mechanical actuators, such a fixation or guard control is achieved by locking the mechanical actuator in a state in which it is inserted into the switch head, for example. Alternatively, a guard control using magnetic force is possible in the case of mechanical actuators, but in particular in the case of electronic actuators. A corresponding guard control system of a safety switch is known from DE 101 46 828 A1.
As a rule, the safety switches are connected to higher-level control systems, to which output signals are transmitted and can also be indicated there on a display. If an operator wishes to know the current state of the safety switch and the guard control for example, the operator does so using the control system.
EP 0 990 835 A 1 discloses a mechanical, electromechanical or otherwise driven device, having of at least two parts that can be moved toward one another and waveguides inside the parts. These waveguides are disposed such that in a specific position, the light waves pass through all partial waveguides and are detected. In the remaining positions, the passage of the light waves is inevitably interrupted.
DE 196 49 593 discloses a locking mechanism for controlling access to working equipment, wherein the locking mechanism has an optical sensor having a transmitter and a receiver. Only when the locking mechanism is in the engaged state, in which the operation of the working equipment is enabled, does the receiver receive coded optical signals that are emitted by the transmitter. The output signal of the transmitter is read into an evaluation device. The operation of the working equipment is blocked or enabled by the evaluation device.
FR 2 684 167 A discloses a device having two connectible profiles made of aluminum. Fiber optic elements are disposed in the two profile pieces such that, when the profiles are connected together, an optical contact bridge is formed.
DE 692 01 486 T2 discloses an electromagnetic closing device having an electromagnet disposed in an elongated, channel-shaped housing. The housing and the electromagnet have elongated projections and/or recesses, which interact with one another such that, with the exception of the longitudinal movement, any movement of the electromagnet is prevented.